Two problems regarding the brain stem of the lamprey will be investigated with electron microscopy. Oculomotoneurons and reticulospinal neurons will be labeled with horseradish peroxidase, and their dendrites will be surveyed in thin sections for the presence of gap junctions. Numbers of axons will be counted in the trigeminal and oculomotor nerves before, during, and after metamorphosis to assess the development of cranial motoneurons.